Fig. 1. Caveolae and caveolin structure. Main panel: caveolae in a differentiated 3T3-L1 adipocyte labelled with an electron-dense marker to delineate the cell surface. Note the uniform size and shape of caveolae (some are indicated by arrowheads) and the numerous caveolae around larger surface-connected vacuoles (asterisks). Lower left: caveolae (arrowheads) in a primary fibroblast shown in a conventional plastic section. Top right: a similar image at higher magnification. Lower right: sheets of plasma membrane from adipocytes labelled for caveolin-1 followed by 10 nm protein-A-gold. Note the unlabeled clathrin-coated structure (double arrowheads). The schematic shows the main features of caveolin association with the plasma membrane; positively charged (+) and aromatic (·) amino acids in the scaffolding domain interact strongly with the membrane; schematic modified from Arbuzova et al. (Arbuzova et al., 2000). Cholesterol may be enriched in the scaffolding-domain-associated portion of the membrane. Bars, 100 nm.